Protein conjugates prepared with HiLyte™ Fluor 488 dyes are far superior to conjugates of fluorescein derivatives such as FITC. Not only are HiLyte™ Fluor 488 conjugates significantly brighter than fluorescein conjugates, they are much more photostable. Additionally the fluorescence of HiLyte™ Fluor 488 fluorophore is independent of pH from 4 to 10. This pH insensitivity is a major improvement over fluorescein, which emits its maximum fluorescence only above pH 10. Extinction Coefficient (M-1cm-1): 70,000 Fluorescence quantum yield: 0.91 Fluorescence Life Time (ns): 4.1